Integrins are a major family of adhesion receptors. They are produced by most cell types and are a means by which the cell senses its immediate environnement and responds to changes in extracellular matrix (ECM) composition. ECM is composed of structural and regulatory molecules, some of which include laminin, collagen, vitronectin and fibronectin, as well as a variety of proteoglycans. These molecules, in cooperation with cell surface receptors, not only provide the basis for structural support, but also contribute to the transmission of biochemical signals from the ECM to the cells interior. Thus, integrins are cell adhesion receptors capable of mediating cell-extracellular matrix and cell—cell interactions. Integrins are implicated in the regulation of cellular adhesion, migration, invasion, proliferation, angiogenesis, osteoclast bone resorption, apoptosis and gene expression (P. C. Brooks, DN&P, 10(8), 456-61, 1997).
The integrin family is composed of 15 α and 8 β subunits that are contained in over twenty different αβ heterodimeric combinations on cell surfaces. Each heterodimers have distinct cellular and adhesive specificities. Integrins bind to extracellular matrix proteins or cell surface molecules through short peptides sequences present in the ligands. Although some integrins selectively recognize a single extracellular matrix protein ligand, other bind to two or more ligands. Several integrins recognize the tripeptide Arg-Gly-Asp (RGD), whereas others recognize alternative short peptide sequences. Combinations of different integrins on cell surfaces allow cells to recognize and respond to a variety of different extracellular matrix proteins (J. A. Varner and D. A. Cheresh, Curr. Opin. Cell Biol., 8, 724-30, 1996).
The αv-series integrins are a major subfamily of integrins. As well as classically mediating cell attachement and spreading, αv integrins are implicated in cell locomotion, in ligand-receptor internalisation, as virus co-receptors, in management of the extracellular protease cascades and as regulators of tumour progression, angiogenesis and apoptosis. The specificities of the five known αv-integrins, (αvβ1, αvβ3, αvβ5, αvβ6 and αvβ8 have been defined and they exclusively recognize ligands via the tripeptide sequence RGD, including vitronectin (αvβ1, αvβ3, αvβ5), fibronectin (αvβ1, αvβ5, αvβ6), von Willibrand factor (αvβ3), fibrinogen (αvβ3) and osteopontin (αvβ3) (F. Mitjans, J. Cell. Science, 108, 2825-38, 1995).
In disease, adhesive function is frequently compromised and results in tissue disorder, aberrant cell migration and dysregulation of signaling pathways. It is well known that alterations in the composition and integrity of the ECM can significantly influence cellular behavior, which in turn may have an impact on a number of pathological processes such as tumor neovascularization, restenosis, arthritis, tumor growth and metastasis. Thus, inhibiting the function of molecules that regulate these cellular events may have significant therapeutic benefit (P. C. Brooks, DN&P, 10(8), 456-61, 1997).
There are at least three major classes of reagents currently being developed as integrin antagonists, and these include antibodies (monoclonal, polyclonal and synthetic) and small synthetic peptides (synthetic cyclic RGD peptides), as well as a family of snake venom-derived proteins termed “disintegrins”. The third major group of antagonists includes nonpeptide mimetics and organic-type compounds.
Integrin αvβ3, the most promiscuous member of the integrin family, mediates cellular adhesion to vitronecin, fibronectin, fibrinogen, laminin, collagen, von Willibrand factor, osteopontin and adenovirus penton base. Expression of this integrin enables a given cell to adhere to, migrate on, or respond to almost any matrix protein it may encounter.
Integrins of the αv subfamily are implicated in tumour development. Integrin αvβ3 is minimally, if at all expressed on resting, or normal, blood vessels, but is significantly upregulated on vascular cells within human tumors. In particular, both vertical progression of the primary melanoma and distant metastases are characterized histologically by an increased expression of αvβ3 integrin (B. Felding-Habermann et al., J. Clin. Invest., 89, 2018-22, 1992). A study involving human malignant melanoma, an increasingly prevalent and aggressive skin cancer, reported the use of monoclonal antibodies to block the αv integrin-ligand interaction which resulted in severely disrupting the development of the tumor (F. Mitjans et al., J. Cell Sci., 108, 2825-38, 1995).
Another important physiological role played by integrin αvβ3 in cancer is within the process of angiogenesis. Angiogenesis, the formation of new blood vessels, allows the cancer to spread and grow. It was shown that blood vessels involved in angiogenesis have enhanced expression of αvβ3 (P. C. Brooks et al., Science, 264, 569-571, 1994; C. J. Drake et al., J. Cell Sci., 108, 2655-61, 1995). It was also shown that preventing the αvβ3 integrin from binding to their ligands caused apoptosis (programmed cell death) in the endothelial cells of newly formed blood vessels and inhibited neovascularization (P. C. Brooks et al., Cell, 79, 1157-64, 1994; M. Christofidou-Solomidou et al., Am. J. Pathol., 151(40), 975-83, 1997; J. Luna, Lab. Invest., 75(4), 563-73, 1996). Thus, antagonists of integrin αvβ3 may provide a powerful therapeutic approach for the treatment of neoplasia or other diseases characterized by angiogenesis.
Another pathological process which involves αvβ3 is coronary restenosis. Surgical trauma and/or injury to blood vessels may lead to the stimulation of smooth muscle cells resulting in an increase migration and proliferation of these cells, which causes an occlusion in the vessel wall and prevents blood flow. Following arterial injury, it was shown that there was early upregulation of integrin αvβ3 at sites of cell accumulation within the vessel wall and that selective blockade of αvβ3 was an effective anti-restenotic strategy (S. S. Srivatsa et al., Cardiovascul. Res., 36, 408-28, 1997).
αv integrins are especially interesting targets since they are implicated in many metabolic processes, such as angiogenesis, bone resorption, cellular migration and proliferation. Consequently, antagonists of αv integrins have great therapeutic potential for diseases such as rheumatoid arthritis, psoriasis, eye diseases (diabetic retinopathy and macular degeneration), restenosis, neointimal hyperplasia, osteoporosis and more particurlarly against tumors, since they simultaneously strike at the developing tumor and at its blood supply (U.S. Pat. No. 5,843,906-WO 9736859/GD Searle & Co; EP 854140/Hoechst AG; WO 9733887-WO9637492/Du Pont Merck Pharm Co; WO 9744333-WO 9737655-WO 9532710-WO 9408577).
There is thus a constant need to find other antagonists of αv integrins in order to provide additional modes of treatments for many diseases that still have no cure. The present invention satisfies this and other need.